Reversible decade counter



2 Sheets-Sheet 1 q IN V EN TORS n. V II Mw 14 QaN'S J. ROSENBERG ETAL REVERSIBLE DECADE COUNTER Dec. 13, 1960 Original Filed NOV. 2, 1955 Ml BY j arme/Eff Dec. 13, 1960 J, ROSENBERG ETAL 2,964,241

REVERSIBLE DECADE COUNTER United States PatentI O REvRsIBLE nEcAnE COUNTER Jack Rosenberg and Alexander F. Brewer, Pacific Palisades, and Thomas J. Scuitto, Santa Monica, Calif., assignors to General Dynamics Corporation, Rochester, N.Y., a corporation of Delaware Original application Nov. 2, 1955, Ser. No. 544,478, now Patent No. 2,833,941, dated May 6, 1958. Divided n and this application Dec. 28, 1956, Ser. No. 631,336

9 Claims. (Cl. 23S-92) This invention relates to electronic counting vcircuits and, more particularly, to an improved reversible decade counting circuit.

In an application by Jack Rosenberg et al. for an Automation System, Serial No. 544,478, filed November 2, 1955, now Patent No. 2,833,941, and assigned to a common assignee, there is described and claimed a system for providing an automatic control for machine tools. There is also described therein a novel and useful reversible decade counter and digital-to-analog con verter. The present application is a division of the Jack Rosenberg et al. application and is directed to the novel, reversible decimal counter and digital-to-analog converter described therein.

The embodiment of the invention employs a glowswitching type of gas tube which is sold commercially by Sylvania Electric Products, Inc., and is known as type 6476. This tube is described in the Sylvania Engineering data service publication 6476. Briefly described, this tube has a common anode, about which are disposed cathodes. Ten of these are called main cathodes; the remainder are called guide cathodes and are classed as first and second guide cathodes. Between each two main cathodes are a first and second guide cathode. The disposition can be considered as main cathode, first guide, second guide, main cathode, etc., around the circle of cathodes. The tube operateson the principle that the ionization, or starting voltage, of gas-filled tubes is lower if ions or electrons are already present yin the anodecathode gap. Under these conditions, a glow discharge can be made to move from one cathode to an adjacent one by means of a relatively small negative pulse on the new cathode, provided that electrons or ions are able to diffuse this new anode-cathode gap. With the series of cathodes about a common anode, a glow-discharge can be made to move in succession along the cathode series by application of successive voltage pulses to each cathode. Thus, the first and second guide cathodes are employed to determine the direction ofthe glow discharge from main cathode to main cathode. With a glow present on a main cathode, first a negative pulse is applied to the adjacent first guide cathode, then a second negative pulse is applied to the adjacent second guide cathode, then, upon the termination of the second pulse, because the main cathodes are biased to a potential below the guides, the glow discharge will be transferred to the succeeding main cathode. If the first negative pulse is applied to the adjacent second guide cathode and the second negative pulse is applied to the first guide cathode, then upon termination of the second pulse to the first guide cathode the main glow will be transferred to a preceding main cathode.

Within a beam-switching tube all first guides are connected together and brought out to a first guide terminal. All second guides are connected together and brought out to a second guide terminal, The order of application of a first pulse and a second pulse respectively to the first and second guide output terminals determines whether 2,964,241 `Psi-tenten Dee. 13, o

r. 1C@ l within a'beam-switching tube the count advances or regresses.

While it can be readily seen that operation of a single stage decimal counter employing one of these gas-beam tubes is a simple affair, complications are presented when yit is attempted to couple a plurality of these gas tubes to form a multi-stage reversible decade counter with a capacity to count hundreds, or thousands, or even greater. These complications arise because of the necessity for applying two pulses from a lower to a higher order decade to effectuate carryover when the lower decade count exceeds nine and also to effectuate a negative carryover (subtraction) when the lower order decade passes through the ten count to the nine count. By way of example, using a decimal and tens order decade tube, if a count of nine has occurred, the tens decade must be made to go from a zero to a one count or not, depending upon Whether the next first and second pulses being applied have an order to add or subtract from the count of nine. Also, using another illustration, if the count of 2O has occurred, it must be known whether the units and tens decade are to be advanced to the count of 21 or to the count of 19, in accordance with the information contained in the incoming first and second pulses.

An object of the present invention is to provide a novel interstage coupling means between glow-switching gas tubes to provide a novel, reversible decade counter consisting of a plurality of decade stages.

vAnother' object of the present invention is to provide a novel and useful reversible decade counter consisting of a plurality of decade stages.

Another problem is presented when the count in the reversible decade counter becomes negative. A way Ain ust then be found for efiectuatin'g a subtraction with positive input counts and an addition with negative input counts. This is further complicated by the fact that two pulses are required for advancing or regressing the count in the counter. Accordingly, a further object of this invention is to provide a unique arrangement for sensing and storing the polarity of the count in the counter and controlling the sense of any input applied to the counter in accordance with the sign of the count in the counter.

Another object of the present invention is to provide a unique arrangement whereby a reversible decimal counter may be employed to provide a digital-to-analog conversion.

Yet another object of the present invention is the provision of a novel arrangement whereby the same circuit which indicates the sign of the count in the counter controls the digital-to-analog conversion arrangement in accordance therewith.

These and other objects of the present invention are achieved in a reversible decimal counter wherein each decade stage comprises a gas-beam-switching tube. Each decade has' a first and second input guide terminal. In order to advance the count of a decade, a first and second pulse in sequence are respectively applied to the first and second guide input terminals. To reduce the count in a decade, a first and second pulse are respectively applied to the second and first guide in the decade. All the second guides of the plurality of decades are connected together. Accordingly, a second pulse is applied to the second guide of all the decades simultaneously.

An interstage coupling arrangement is provided between each two decades wherein, when the lower decade 'is in the nine count condition and a first and second pulse are respectively applied to the first and second guides of this decade, a pulse is applied to the first guide of the succeeding, or higher, decade before the pulse is applied to the second guide of the higher decade. In response to the lower decade being in the zero count condition and a pulse being applied to the lower decade ksecond guide before the application of a pulse to the first guide, a pulse will be applied to the rst guide of the succeeding, or higher, decade after the application of a pulse to its second guide.

A memory is provided which, when the entire counter is at zero, senses the sign of the next count being entered into the counter. From this, it stores and indicates the sign of the count in the counter. Gating means are provided at the input of the counter which are controlled by the memory means to apply a rst and second input pulse to the counter in a manner to add to or subtract from the count in the counter which is resolved by the information contained in the memory as to the sign of the counter count and the order of the application of the rst and second pulses. Furthermore, a digital-toanalog conversion resistance ladder is provided for each decade, the output of which is applied to circuitry which is controlled responsive to the memory to provide an analog output indicative of the count and also having a polarity which is determined by the memory.

The novel features that are considered characteristic of this invention are set forth with particularly in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following descirption when read in connection with the accompanying drawings, in which:

Figures l and 2 comprise a circuit diagram of an embodiment of the invention.

As describedpreviously, the invention herein employs a glow-switching type of gas tube which requires the application thereto of two pulses in order to advance or regress the count. Figures l and 2 show a circuit diagram of an embodiment of the invention employing two decades. This should not be construed as a limitation because from the description employing two decadesk it will become readily apparent how any number of decades required may be connected together and still be within the spirit and scope of this invention.

It should be noted that Figures l and 2 herein are identical to Figures 16A and 16B in the previously noted application to Rosenberg et al. In that application, the arrangement was employed as an error register, wherein pulses commanding motion and pulses responsive to motion commands having been executed are combined and applied to the counter so that the resultant count will be positive if the total number of command pulses exceeds the total number of response pulses. The output of the counter is converted to an analog voltage which controls subsequent apparatus to operate in a direction to provide pulses to reduce the count in the error register to zero.

The two figures of the drawing herein actually constitute a single circuit, and not two separate circuits. In order to identify the same leads which connect apparatus in one igure of the drawing with apparatus in the second figure of the drawing, the leads are brought out to the side of the drawing and have assigned letters thereto which correspond.

Input terminals 6 and 8, respectively also assigned letters G1 and G2, provide terminals to which a first and second pulse may be applied, either in that sequence or in a reverse sequence to be added or subtracted from the count in the counter. Terminal 6 is connected to the two cathodes of a double triode tube 1U. One side of this double triode tube is referred to as 10A and the other side as 16B. Terminal 6 is also connected to Figure 2 of the drawings along a lead designated by the reference letter 0. Input terminal 8 is connected to two cathodes of a double triode tube 12, having each of its triodes respectively designated by 12A and 12B. Input terminal 8 is also connected to the apparatus in Figure 2 of the drawing by a lead having applied thereto the reference numeral N. These latter connections will be described further subsequently.

Tubes 10A and 12B have their anodes connected tof gether and brought up to be connected to the grid of tube 14B in a double triode tube 14. A clamping diode 15 and a biasing triode 17 are employed to establish the most positive signal level to which the grids of tubes 14A and 14B can be driven. This positive clamping arrange-- ment is eectuated by connecting the grid of tube 17 toV a voltage divider 23, connected across the operating potential supply. Tube 17, which is connected as a cathV ode follower, is thus biased to be in a conducting condi tion. Its cathode thus is maintained positive and is coupled to the diodes 15A and 15B of double diode 15. The cathode of diode :15B is connected -to the grid of tube 14B; the cathode of diode 15A is connected to the grid of tube 14A. Under quiescent operating conditions, the value of the positive bias applied to the grids of tubes- 14A and 14B by means of the voltage dividers to which these grids are connected has a sutcient amplitude soA that no conduction occurs through diodes 15A and 15B. Upon the application of a negative-going signal to either' of the grids of tubes 14A or 14B, which lowers the potential of either of these grids to the point where the diode 15A or diode 15B begins to conduct, the grid will be eiectively clamped to the potential of the cathode of tube 17 and will go no further negative. Tube 14B is a cathode follower and has output from its cathode coupled 4to the cathode of tube 16B in double triode tube 16. In response to input, tube 16B provides an output pulse which is applied to the guide 1 input terminal of a decade glow-switching gas tube 18. This terminal is also labeled G1. Tubes 10B and 12A have their anodes connected together and brought up to the side 16A of the double triode 16. Side 16A is also cathode-follower connected, and output from its cathode is applied to all the guide 2 terminals of all the gas tube decades 18, 22 employed in the gas tube counter. The guide 2 output terminals of all the decades are connected together over lead B.

It should be noted that the control grids of tubes 10A, 10B and 12A, 12B are direct-coupled through resistors to the control grids of a ip-op circuit 20. The flip-dop circuit 2t) includes two tubes, respectively designated as 20A and 23B. The potential of the control grids of tube 29A establishes the potential at the control grids of tubes 10B and 12B. The potential at control grid of tube 20B establishes the potential at the control grids of tubes 10A and 12A. Thus, the state of the ip-tlop will determine which sides of the double triode tubes 10 and 12 can become conductive when an input pulse is applied to the cathodes of those tubes from the first and second input terminals 6 and 8.

Flip-ilop 20 is the well-known two-tube type of iiip-tlop circuit having two stable states with the anode of one of the tubes connected to the grid of the other and the anode of the other of the tubes connected to the grid of the one. It may be driven from one to the other of its stable states by the application thereto of pulses. Fliptlop 20 serves as a memory to store the sign of the count which is held in the decade counter. The manner of its being driven will be described subsequently.

For the purposes of explaining the operation of the input gating means, including double triodes 10 and 12 in response to the sign-storing ip-op 20, let is be assumed that ip-op 20 is in a stable condition wherein triode 20A is conducting. When this occurs, there is a positive signal on itsgrid which is applied thereto from the plate of tube 20B. This Ypositive grid signal is also applied to the grid of tubes 12B and 10B. Assume that a negative signal is applied first to input terminal 6 and thea to terminal 8. This will enable tube v10B to conduct rst, followed by tube 12B. The output of tube 10B is applied to tube 16A` The output from the cathode of tube 16A is applied to guide 2. The output of tube 12B is applied to tube 14B. The output of tube 14B is applied to tube 16B, the output from which is applied to guide 1. The

counter. is ythus made to subtract, since the guide 2 pulse precedes the guide 1 pulse.

Assuming the same state ofthe flip-flopv 20, the application of a pulse to input terminal 8 before the application of a pulse to input terminal 6 will cause tube 12B to become conductive before tube B. Therefore, a guide 1 pulse will be received at the counter before the guide 2 pulse. I

It is thus seen that when flip-flop 20 is in a stable condition with its tube 20A conducting, the'order of application of a first and second pulse applied to the input terminals is reversed when they are applied to the counter tubes.

Assume now that flip-flop 20 is in condition with the tube 20B conducting and tube 20A not conducting. Tubes 10A and 12A are enabled, so that when a first and second pulse are applied to input terminals 6 andl 8, these tubes will do the conducting. Thus, the application of input pulses to terminal 6 first and then terminal 8 results in first tube 10A becoming conductive and then tube 12A. .Tube 10A drives tube 14B, the output of which is applied to guide 1 through tube 16B. Tube 12A drives tube 16A, ,the outputof which is applied to guide 2. Assuming the same stable condition on the part of Hip-flop 20, then the application of a pulse first to input terminal 8, followed by the application of a pulse to input terminal 6. will result in. arpulse being first applied to the guide 2 terminal, followed by a pulse being applied to the guide 1 terminal.

Thus, with the flip-flop 20 in its second stable condition, .or the one inst described. guide 1 and guide 2 of the counter tubes will receive pulses in vthe order of application grespectivelvto input terminals 6 and 8, or respectively 4G1' and G2. -Ifvflip-op 20 is inits other stable-state, vthen guide l and guide 2 of thev4 counter tubes will re- -ceive pulses. the order of which is in reverse to the order of their application respectively to input terminals G1 and G2. v

The gas tubes 18` 22 have their ten main cathode numbered from O to 9. Their guide cathodes are not shown tomaintain clarity-in the drawingsa Tube 18 has Ja single anode 1'9. and tube 22 has a single anode 23. -As shown in the drawing. in each counter tube a resistor 21 is inserted in series with each of the cathodes which are numbered from 1 through 0. When an arc exists .between an anode-and aparticular cathode. the current being drawn causes a voltage of approximately `+35 volts .to exist at the cathode. By connecting separate resistors `25 between the cathodes and tapping olf at one end of the resistive ladder thus created, a voltage may-be obtained which is the analog of the count in the counter.

yTo explain this, assume, for example, thatvan `arc exists at cathode 2'. At a tapoi point on the cathode 8 there will be a lower value of voltage than if an arc existed at cathode 7. The reason, obviously, is because there is vmore resistance between `cathode 2 and the tapoff point,

at cathode 8 than there is between cathode 7 and the `tapoff point. f The values for the resistors in the resistance ladder, :as well as for the cathode resistors to provide fairly dis- Icrete steps of the ana-log voltage are shown in the draw- Y,

ing. These are not to be construed as a -limitation, since .iother values may be employed which may function .equally well. However, these values were used in an .embodiment of thel invention which was built and oper- :ated satisfactorily. Cathode 8 and cathode 9 are respecf-tively coupled to a common point on lead G through a :resistor 27 and through a diode 29. The operation of the digital-to-analog converterwill be described in fur- :ther detail subsequently herein.t

-Thecircuitry to be described nextis that for the inter- :i1- couplingl arrangement between thedecades. This inter coupling arrangement- -may be employed betweenx s uc- `cessive decade stages. The output from cathode` 9. of fthe lower decadevstage 18 is connected over lead E to gthfjd Qf tube- 2 4A- 'BQFWQQnthe tube grid and ground succeeding count stage. lto all guide 2 terminals simultaneously. Thus, the suc- .ceeding decade is made to add a count.

:diodes as long as these pulses last.

employed to maintain the voltage provided by the cathode 9 output for an interval required to insure the operation of the subsequent circuitry, since the transition of the nine-count stage can be too rapid. The anode of tube 24A is connected to the anode of a fiip-ilop tube 30B. Flip-flop 30 is the same type as flip-flop 20. Tube 24A is coupled to fiip-iop 30B as a plate follower. In other words, when tube 24A is rendered conductive by receiving a sign-al both on its grid and on its cathode, it pulls current through the anode load of tube 30B,

whereby tube 30B may be made to become conductive.

.counter stage 22. An add ,1 input applied to counter tube 18 when it is in its ninth count condition requires a carryover to counter tube 32, since it is necessary for -tube 18 to go to its zerocount condition and tube 22 to go to its one count condition, representative of the .number l0. To switch` tube 22 from its zero to its one count condition, it is necessary to apply a pulse to its guide 1 terminal, followed by a pulse to its guide 2 terminal, To enable the addition of a count into tube '18, it is necessary for it to receive a guide l pulse fol- -lowed by a guide 2 pulse. Thus, if the first pulse being appliedto tube 18'is received from tube 14B, this first pulse is also applied over lead F to enable tubes 24A and 32A to conduct to provfde the guide 1 pulse to the The following pulse is applied When a count is to be subtracted, the pulse destined for the guide 2 terminal of the counters occurs first, then a guide l pulse. This removes the glow from main cathode 9 to a guide cathode. Thus, at the time a signal is received over lead F no signal is being received from `main cathode 9, and the charge on condenser 28 has leaked off. For the situation where arst guide terminal pulse occurs first (carryover required), the conduction of tube 24A occurs. either While the `glow is still at main cathode nine or so"s'hortlyi'after it has been transferred from main cathode nine to the'adjacent guide l that the voltage on the grid of 'tube 24A is still maintained by condenser 2 8.

`For resetting flip-flop 30 after it has been operated, another plate follower tube 48B is employed. This tube has its anode coupled to the anode of tube 30A, and thus when tube 48B conducts it causes tube 30A to conduct, which is the standby or reset state of iiip-op 30. Tube 48B is controlled to be conductive except during the interval when first and second pulses are present. This is arranged by connecting the Vgrid of tube 48B over lead Ito the anodes of' a double diode 40. The anodesv are connected through a resistor 46 to' a source of positive potential. One cathode 44 is coupled through resistors to the anodes of tubes'10B and 12A; The other cathode 42 is coupled through resistors to the anocles of tubes 10A and 12B. A first and a second pulse received from these gating tubes causes current to be drawn through these They are made to have some small overlap time, and therefore current is d'rawnthrough the resistor 46 during the first and second 'Thusfatfthe termination of the first and second pulses the double diode 40 no longer conducts and tube 48B Ican reset the lflip-flop, 3,0.

anemia 'The interdecade 'stage coupling circuit-also performs `the function of subtracting a count from the succeeding decade when the preceding decade goes from a -zero to a nine condition. Regarding Figure l, it will Vbe seen that the zero main cathode is coupled tothe grid of tube 24B. Tube 24B has its anode coupled to the anode of tube 24A, which is also connected to the anode of tube 30B of the flip-flop. Thus, when the zero count condition occurs, a positive signal is applied to the grid of tube 24B. It, however, cannot conduct until it receives a negative signal upon its cathode. This'is received over the lead labeled lL which is coupled to thecathode-follower tubeY14-A. The control grid of tube 14A is coupled to the control grid of tube 16A, the output of which is applied to the guide 2 terminals of all the decades. Thus, upon the' appearance of a guide 2 pulse preceding a guide 1 pulse subsequent to the decade 18 reaching its zero count condition, tube 24B is rendered conductive, driving the iiipflop 30. The second guide lpulse which has initiated the operation of the flip-Hop 30 has been applied to the decade 22 prior to the application thereto of a first pulsefrom the tube 32A, since the tiip-flop acts to provide the necessary delay. Therefore, when the decade 18 is in its zero count condition and a count is to be subtracted, the interstage coupling circuitry subtracts a count from the subsequent decade 22. After the termination of the first guide pulse, the ip-op 30 is reset by tube 48B in the manner described previously.

Next there will be described the arrangement whereby the ip-flop 20 is enabled to store an indication of the sign of the number of the counter. Tube 48A has its grid connected between two resistors 54'and 56. Resistor 54 is connected over lead J to the zero ycathode in decade 18. Resistor 56 is connected to the zero cathode in decade 22. Tube 48A is biased so thatit will become conductive only when the glow exists in decades 1'8'and 22 at both zero cathodes. Tube 48A is connected as a cathode follower, and when it becomes conductive, its output is applied to the grids of tubes 58A and 58B. -Because of the possibility of a rapid transition of the zero count, a condenser 60 maintains for a time the voltage from the cathode of tube 48A applied to the grid of tube 58B. The anodes of tubes 58A and 58B are connected through neon indicator tubes through separate resistors to ground. The anode of tube 58B is also connected over lead Kto the anode of tube 20B in ip-op 20 and the anode of tube 58A is connected over the lead L to the `anode of tube `29A in flip-flop 2d. It is thus seen that tubes 58A and 58B are plate-follower connected to tubes 20A and 20B, respectively. However, neither tube 58A nor tube 58B is able to conduct unless a negative signal is applied to its cathode. The cathode of tube 58A is connected over lead N to input terminal 8 (G2) and the cathode of tube 58B is connected over lead O to input terminal 6 (G1).

The operation of this system therefore is as follows: when all decade stages in the counter are at their zero count condition, then tube 48A is enabled to conduct. It applies an output from its cathode to the grids of tubes y53A and 58B. Neither of these tubes, however, can conduct unless a negative pulse is applied to their cathodes. These negative pulses consist of the first and second guide pulses which are being applied to the counter. If it is desired that the counter advance its count as previously described, a first guide pulse is received at G1, followed by a second guide pulse at G2. The rst guide pulse on input terminal 6 is applied over lead O to the cathode tube 58B. This causes tube 201B in ilip-op 20 to become conductive, thus storing the fact that the counter has 3a positive count. Tubes 10A and 12A in the input-gating arrangement are enabled, whereby the first guide pulse is applied to the rst guide input terminal from tube V16B and the second guide pulse which occurs subsequently is applied to the second guide input terminal of thedecades. By the time the second guide pulse arrives, the rst guide pulse has been applied to the glow-switching tube 18 and 8 the glow-is shifted'from'the zero cathode -tothe Vrst guide cathode adjacent thereto. Therefore, #tube 48A A is no longer conductive Aand there is vno vlonger a'signal being applied to the grid of tubes 58A and 58B. Tube 58A will therefore notbe rendered conductive by the succeeding second guide pulse.

Assume now that vall the decades are in their zero count condition and a positivepulse is being applied to the control grid of tubes 58A andSSB. vAt' this time it is desired to apply a negative count 'to the counter. Therefore, a second guide pulse is first applied to terminal 8 and a first guide pulse issubsequently applied to terminal 6. At the time the second guide pulse arrives, it is applied 'over lead N to the cathode of tube 58A, enabling it to become conductive. As a result, tube v20A is made conductive by the plate follower action of tube 58A. Tubes 10B and 12B are enabled by flip-op 20. The pulse on terminal G2 is therefore applied through tubes 112B, `14B and 16B to the first guide input lterminal of decade 18. The pulse -on terminal G1 arriving subsequently is appliedthrough tube 10B and tube 16A to the second guide input terminal ofthe decades. Thus, when `flip-flop 20 indicates that the count Vis negative, ,any subsequent negative count inputs increase the count in the counter and any subsequent positive count inputs decrease the count in the counter. Thus, the effect ofthe sign ip-'tlop 20, when it indicates a negative count, is to reverse the order of the pulses which are applied to input terminals 6 and 8.

It is thus seen that tube 48A lfunctions to sense when the decades are in their zero count condition. Tubes 58A and 58B function to determine by the order of the first and second guide input pulses thereafter applied whether or not the sign ofthe countis positive or negative, and with this informationip-flop 20 is set to vstore the proper indication. Flip-flop 20 controls the input gating Ymeans 4so that first andfsecond guide pulses are -analog conversion -of the counts -in the decade counter. It will-be noted that a plurality ofv resistors 25 are connected in aladder between the cathode-load resistors of the respective decade tubes 18 and 22. The values provided for these resistors are selected for a suitably operating'digital-to-analog conversion and are not to be considered as the only ones possible. These were the ones which were employed in'an operative embodiment of the invention. In decade 18 the connection between the eighth and ninth main cathodes includes two resistors and a diode 29. The reason for the use of this diode is to isolate the main cathodes preceding the ninth from the grid of tube 24A. The cathode of the diode 29 is connected over a lead G to the control grid of a tube 32B. Tube 32B has resistors 73, 75, 76 and a potentiometer 74 connected in series between ground and its cathode.

The movable arm of the potentiometer 74 is connected to all the cathode load resistors 21 of the main cathodes of the decade 22. As previously noted, tube 22 also has a resistance ladder formed by connecting a resistor 25 between each two main cathodes. The end of this resistance ladder on main cathode 9 is connected to `the grid of a tube A and to the grid of another tube e voltage o n lead G, which is an analog Arepresentation of that count. This occurs since, as previously described, the resistance ladder which is employed will have a voltage on the order of 35 volts applied thereto at any one of nine contact points, as determined by the location of the glow at any one of the nine cathodes. A tapoff is made at the ninth cathode end of the ladder. Therefore, the amplitude of the tapol voltage increases as the count approaches nine. This analog voltage is applied to the grid of the tube 32B, to render it conductive to a degree determined by the amplitude of the input to its grid. The voltage across the potentiometer 74 is determined by the signal which is applied to the grid of the tube 32B. Decade 22 draws the glow current required for itself through potentiometer 74. The potential at the potentiometer 74 is established by the conductive condition of tube 32B. Therefore, the voltage which is applied by lead 74 to the grids of tubes 80A and 80B is the sum of the Voltage derived from the decade 18 resistance ladder, plus that from the decade 22 resistance ladder. Tube 32 serves to raise the voltage due to the count in decade 22 by the amplitude of the voltage due to the count in decade 18.

Referring now to Figure l, it will be seen that output from the memory flip-flop 20 is applied along leads M and P to the respective grids of two tubes 82A, 82B. These vtwo tubes are cathode followers and have their outputs respectively applied through two diodes 84B and 84A to the respective grids of tubes 80B and 80A. The signals .derived from the cathodes of tubes 82A and 82B are only positive ones, since negative signals are clamped to ground by the double diode clamp 83 connecting these leads to ground. Since the output of the flpdiop 20 will consist of both a negative and a positive signal, the cathodes of neof the two tubes 82 will be positive and the other cathode will be negative. The positive cathode will block the conduction of its corresponding diode 84A or 84B and the negative cathode will enable conduction of the corresponding cathode to ground. In this manner, one of the grids of the tubes 80A and 80B will be con* nected to ground by the one of the cathodes 82A, 82B which is negative. The other of the grids of the tubes 80A, 80B will be able to respond to the positive signal received from the lead 72.

Y Assume forillustrating this operation that the flipflop 20 has tube 20A conducting and tube 20B not conducting, apositive signal is applied along lead P to the grid of tube 82A and a negative signal is applied along lead M to the grid of tube 82B. The cathode of tube 82A goes positive and will therefore block conduction through diode 84B. The cathode of tube 82B goes negative and therefore conduction of tube 84A is enabled and the clamping diode then places the cathode of tube 844A at ground. Accordingly, the signal received from lead 72 will be applied to the grid of tube 80B, since, effectively, the grid of tube 80A is connected to ground. AsA a result of the tube 80B being enabled to conduct, an output is derived from its anode which varies in a negative direction in response to an increase in the analog signal applied to its grid. This is as it should be, since when the side 20A of flip-flop 20 is conductive, this is indicative of the fact that a negative count is in the counter. When side 20B of the flip-flop is con'- ducting, indicative of the fact that a positive count is in the counter, then tube 82B receives a positive signal, cutting'off diode 84A and enabling grid 80A to follow the signalbeing applied to it froml lead 72. The common cathode coupling resistor 94 applies the signal'whic'h is ybeingV applied to the grid of tube 80A to tube 80B. Its output follows the signal, and a positive-going volt age lis derived at the output potentiometer 96, which is the Ianalog ofthe positive digital countfinthe counter.A Therefore, .the polarity of the outputY .analog voltage .controlled by the sign of the count in the counter uhih'isstored inthe Hip-flop 20 v .f f l i l() The double-pole, double-throwvrelay .100 seifvesythe function of enabling a resetting of the counter to the .zero count condition. It does this by opening the cathode connection to ground of the zero cathode of the decade 22, which is also connected to the zero cathode through a coupling resistor of decade 18. The plates of the various decades are then connected to the i-lSO volt source, instead of the 400 volt source. With this arrangement, the decade gas tubes have their zero cathodes connected to B and, therefore, the glows will be switched to the zero cathodes. To summarize the operation of the decade counter, a first and second pulse are applied to the G1 and G2 input terminals. The order of the frstyand second pulse applied to these input terminals indicates whether or not the count should be added to the count in the counter or is subtracted from the count in the counter. A memory circuit, which is the flip-flop 20, serves the function of storing the sign of the count in the counter so that gating means, consisting of the tubes 10 and 12, may be enabled in a manner to enable the properaddition or subtraction of the count by controlling the; interconnection between the G1 terminal to the first: guide input terminal in the gas tube decade counters and? the G2 terminal to the second guide input terminal in;

the gas tube decade counters. An interstage coupling; arrangement is provided whereby between each twoi `decades there is provided a flip-flop circuit which, when.l a preceding decade has the proper count, is set in a condition to apply a first guide pulse to the subsequent decade before or after a second guide pulse if the next .count to the preceding decade warrants this operation. If not, then the interstage flip-flop is reset. lMeans are also provided in the form of resfstance ladders connected between main cathodes of each decade whereby a digital# toanalog conversion of the count is en; bled. The analog voltages of the various decades are in effect added by means of a cathode follower, and the resultant analog voltage is either presented at an output terminal in a positiveor negative-going direction in accordance with the sense of the count in the counter. The memory flipflop establishes the polarity sense of the analog voltage.-

Accordingly, there has been described and shown herein a novel, useful, reversible decade counter and digital-to-analog converter. We claim: 1. A reversible decade counter having 'a plurality of decade stages each of which includes a gas flow-sw tch-L ing tube of the type having a first and a second guide terminal the advance or regression of a count being obtained by the order of application of a first and second pulse respectively to said first and second guide terminals, means for applying a first and second pulse to a first of said plurality of decades, means for coupling all the second guide terminals of all decades together, interstage coupling means between decades each includ-' ing means for applying a first pulse to the first gud'e terminal of a succeeding decade prior to a sec-ond pulse to the second guide terminal of said succeeding decade responsive to a preceding decade being in its ninth count condition and the application thereto of a first pulse fol-- lowed by a second pulse, and means for applying a first pulse to the first guide terminal of said succeeding; decade subsequent to a second pulse to the second'guide-y terminal of said succeeding decade responsive to said. preceding decade being in itsy zero count` condition andi the application thereto of a second-pulse followed by a, firstpulse.'

2."A reversible 'decade counter having apluralityofA decade stageseajchof which includes; a' g'as'glow.svvitcli-iA ing', tube of the-"type-having a first 'and a secondV guide terminal, the advance or regression Iof'acount being, obtained bythe'order of application of a'first andl secondi p ulse respectively lto saidfirst'fand`j second guide ter- Initials; means fer applying first fand'.- second pulses' to; gli

Erst decade, meansfor coupling all said second guide vterminals together, ka coupling arrangement between "decades includinga fiip-flop circuit having a first and -second stable state, a first means for driving said flip-flop from its first to its second stable state responsive to said first decade being in its ninth count condition and the application thereto of a first pulse preceding a second pulse, a second means for driving saidflip-fiop from its first to its second stable state responsive to said first decade being in its zero condition and the application thereteo of a second pulse preceding a first pulse, means to apply output from said flip-flop in its second stable state to the first guide terminal of a decade succeeding Vsaid first decade, and means responsive to the application of a first -pulse or a second pulse to said first'decade to reset said Hip-flop.

3. A reversible decade counter having a plurality of decade stages each of which includes a gas glow-switching tube of the type having a first and second guide terminal, the advance or regression of a count being obtained by the order of application of a first and second pulse respectively to said first and second guide terminals, first and second pulse input terminals, means for coupling the second guide terminals of all decades together, interstage coupling means between 'decades each including means for applying a first pulse to the first guide terminal of a succeeding decade prior to a second pulse to the second guide terminal responsive to the preceding decade being in its ninth count condition and the application to said preceding decade of a first pulse followed by a second pulse, and means for applying a first pulse to the first guide terminal of a succeeding decade subsequent to a second pulse to the second guide terminal responsive to the preceding decade being in its zero count condition and the application to said preceding decade of a second pulse followed by a first pulse, means for storing the sign of the count in said counter responsive to all said decades being in their zero count condition and the order of application of a first and a second pulse to said first and second pulse input terminals, and means responsive to the sign of the count in said means to store to establish the order of the application of first and second pulses from said first and second pulse input terminals to said first decade.

4. A reversible decade counter having a plurality of decade stages each of which includes a gas glow-switching tube of the type having a first and second guide terminal, the advance or regression of a count being obtained by the order of application of a first and second pulse respectively to said first and second guide terminals, first and second pulse input terminals, means for coupling the second guide terminals of all decades together, interstage coupling means between decades each including a first flip-liep circuit having a first and second stable state, a first means for driving said fiip-flop from its first to its second stable state responsive to a preceding decade being in its ninth count condition and the application thereto of a first pulse preceding a second pulse, a second means for driving said fiip-fiop from its first to its second stable state responsive to a preceding decade being in its zero count condition and the application thereto of a second pulse followed by a first pulse, means to apply output from said fiip-fiop in its second stable state to the first guide terminal of a said succeeding decade, and means responsive to the application of a first or second pulse to said first decade to reset said fiip-fiop, a second fiip-op circuit having a first and second stable state, means responsive to all said decades being in their zero count condition and to the application to said first decade of a first pulse followed by a second pulse to drive said second fiip-fiop to a first stable state and to the application to said first decade of a first pulse followed by a second pulse to drive said second ip-fiop to a second stable state, and means responsive to the stable state of said second flip-flop to 12 establish-the order "ofthe-application of first and second pulses from said first -and second pulse input terminals to said first decade.

5. A reversible counter as recited in claim `4 wherein said means to drive said second flip-fiop responsiveto all said decades being in their zero count condition and to the order of application of first and second pulses includes a first cathode follower tube, means coupling said cathode follower tube to all the decades when in their zero count condition, a first and second plate follower tube each having an anode, cathode, and control grid, means to apply said cathode follower tube output to the control grids of said first and second plate followers, means coupling said first pulse input terminal to said first plate follower cathode, means coupling said second pulse input terminal to said second plate yfollower cathode, and means coupling said first and second plate follower anodes to said second fiip-fiop circuit to drive it to its first or second stable condition responsive to whichever of said first and second plate follower tubes is rendered conductive.

6. A reversible decade counter as recited in claim-4 wherein said means responsive to the stable state of said second fiip-fiop to establish the order of the application of said first and second pulses from said first and second input terminals to said first decade includes first, second, third, and fourth coincidence gates each requiring a coincidence of their inputs to provide an output, means for applying the output of said first and third gate to the first guide terminal of said first decade, means for applying the output of said second and fourth gate to the second guide terminal of said first decade, means to apply output from said second flip-flop in its first stable state to said first and third gates, means to apply output from said second fiip-fiop in its second stable state to said second and fourth gates, means to couple said first input terminal to said first and second gate, and means to couple said second input terminal to said third and fourth gates.

7. A reversible counter as recited in claim 4 wherein each decade stage includes an anode and ten main cathodes, a separate load resistor in series with each of said cathodes, a plurality of resistors, means for coupling a different one of said resistors between adjacent ones of nine of said main cathodes to form a resistance ladder, means for combining the voltages existing across the resistance ladders of all said decades in said counter, and means responsive to the stable state of said l second flip-flop and to the output of said means for combining to provide an output having an amplitude and polarity which is an analog representation of the count in said counter.

8. A reversible decade counter having a plurality of decade stages each of which includes a gas glow-switching tube of the type having ten main cathodes, and a first and second guide input terminal, the advance or regression of a count being obtained by the order of application of a first and a second pulse respectively to said first and second guide terminals, means for applying first and second pulses to a first of said plurality of decades, means for coupling all the second guide terminals together, interstage coupling means between each decade for advancing the count of a succeeding decade responsive to a preceding decade being in its ninth count condition and the application thereto of a first pulse before a second pulse and for regressing the count in said succeeding decade responsive to said preceding decade Ibeing in its zero count condition and the application thereto of a second pulse before a first pulse, means to establish .the sign of the count in said counter, a plurality of cathode load resistors, a different one of which is in series with a different main cathode in each gas tube, a plurality of coupling resistors for each gas tube, means for connecting a different one of said coupling resistors between two adjacent ones of nine of said cathodes to form a resistance ladder, means for combining the outputs of the resistance ladders of all the gas tubes in said counter, and means responsive to the combined resistance ladder outputs and to the sign of the count established in said counter to provide an output which is an analog representation of the count in said counter.

9. A reversible decade counter as recited in claim 8 wherein said means responsive to the combined resistance ladder outputs and to the sign of lthe count established in said counter to provide an output which is an analog representation of the count in said counter includes a lirst and a second tube each having an anode, cathode, and control grid, a load resistor connected to the anode of said rst tube, a common cathode load resistor coupled to both tube cathodes, a source of negative potential, an output resistor connected between said rst tube anode and said source of negative potential, an output terminal connected to said output resistor, means to apply the output of said means for combining to the grids of said rst and second tubes, and means responsive to said means to establish the sign of the count establishing a positive sign to clamp the first tube grid and establishing a negative sign to clamp the second tube grid.

References Cited in the tile of this patent UNlTED STATES PATENTS 2,473,159 Lyman `Tune 14, 1949 2,679,978 Kandiah June 1, 1954 2,810,099 Townsend et al. Oct. 15, 1957 

